CN114450728A - Device for displaying information and for capturing imprints of a limb - Google Patents

Abstract

The invention relates to a device for displaying information by means of reflection and for simultaneously recording skin imprints on a plurality of blood-flowing skin areas of a person's limb by contact. Seen in the direction of the skin area in contact, the device comprises: a placement surface (2) for placing the limb; a touch-sensitive layer (4), the touch-sensitive layer (4) registering whether a skin area is placed on the placement surface (2); an LC cell (5), the LC cell (5) having pixels (6) arranged in a grid-like manner which are individually controllable by means of a control unit; a lighting unit having a transparent light guiding layer body (7) and first and second lighting devices; and an optical sensor layer (8) arranged below the light-guiding layer body (7) and having sensor elements (9) arranged in a grid pattern. The first illumination means is configured for illuminating the LC cell (5) with diffuse light in a first wavelength range, and the second illumination means is configured for emitting directional light in a limited angular range around a predetermined central angle not exceeding 20 ° and in a second wavelength range. The sensor element (9) is sensitive to light of the second wavelength range. The pixels (6) of the LC cell (5) are switchable between a state transparent to the diffuse light and the directed light and a state opaque to at least the diffuse light, the light being illuminated by the diffuse light emitted by the first illumination means to display information.

Description

Device for displaying information and for capturing imprints of a limb

Technical Field

The invention relates to a device and a method for displaying information and for simultaneously capturing imprints (Abdr üken cken) of a plurality of blood-circulating skin areas of a limb (typically a finger) of a person on the basis of contact. Reflections of limbs (Autopodien) on the underlying surface are used to generate the acquisition of the imprint, for example, disturbed reflections can be used

Principle of total reflection.

Background

The development of mobile phones over the last years into devices that manage more and more sensitive data has also placed higher demands on the secure authentication of users. The security of authentication is also important to the user itself. Here, in addition to entering a password or code, biometric authentication by means of a user's personal characteristics is becoming increasingly popular. Known methods are based on face recognition, for example. However, biometric authentication by means of finger prints provides more information and thus higher security, since the information encoded in the papillary structure of a human finger is for example significantly more than what can be checked by biometric authentication by facial recognition.

Authentication by means of a single finger print has long been available and mobile phones suitable for this purpose usually have a single finger placement position separate from the rest of the display. In this case, a plurality of stamps can also be stored in the database, but only a single stamp can be registered at the same time. Multi-finger authentication, in which the print of a plurality of fingers is registered at the same time, provides higher security. Such registration is made through the display of the handset for space and ergonomic reasons. Here, sensor display screen combinations already exist in mobile devices, wherein an optical image sensor (CMOS, TFT, CCD sensor, etc.) is connected to a display screen (OLED, QLED, LCD display screen, etc.). In order to enable display screen input by a finger, in most cases, a touch-sensitive layer is integrated in the display screen.

The optical image sensor collects skin prints, compares the skin prints with data stored in the system to determine and confirm the identity of the user if necessary, or to trigger certain functions of an application that may be associated with certain fingers.

In other devices known from the prior art, the touch-sensitive area of the display screen simultaneously serves as a resting surface for the finger whose imprint is to be captured. Thus, no separate area remote from the display screen area is required to acquire the biometric features. In this way, the effective area for displaying information can be increased, since a separate sensor area for placing a finger is no longer required.

Here, an optical image sensor is preferably used, which has the following advantages compared to capacitive or ultrasound-based finger print sensors: high-resolution acquisition can also be achieved with these sensors over a large distance between the optical sensor and the biological object to be acquired. This is important, for example, when a user of the mobile device applies other cover films or cover glasses to the display screen surface, for example, to prevent scratching. Liquid Crystal (LC) display panels are mainly used as display panels (hereinafter also referred to as "displays") because they are manufactured at low cost and are durable.

For example, reference is made herein to WO2019/041214A1 and US2018/0165497A 1. In addition to the usual display screen illumination, additional illumination devices arranged laterally are used here, which illuminate the skin area placed on the display screen with directed light. The light of the additional illumination means reflected back from the skin area is then detected by an optical image sensor located below or integrated into the display screen. For displaying information on a display screen, LC cells are generally used which are equipped with a planar backlighting, wherein the optical sensor is located in front of the opaque backlighting, as seen from the direction of the viewer, and must itself be transparent, wherein the brightness loss still exists in the range above 50%. The light emitted by such background illumination means propagates diffusely, and the structure of the skin print is often not resolved with sufficient accuracy in this way, wherein the greater the distance between the sensor and the placed object, the lower the resolution. In order to illuminate the placed skin area with directed light, the assembly therefore has said additional illumination means, which are arranged laterally beside the background illumination means, wherein the light of the additional illumination means is coupled into its own light guide arranged above the LC cell. This reduces the sharpness of the display screen and the displayed image or information appears less sharp, because by means of the additional illumination layer, the light guide, on the one hand the distance between the LC cell and the top of the cover layer is increased, and on the other hand additional light scattering structures and layers or other boundary surfaces are arranged in the light path. Furthermore, the additional illumination device is disadvantageously designed such that the entire placement surface cannot be illuminated with the same light intensity as the directed light, so that only a part of the display screen surface can be used to accommodate the high-resolution skin impression; simultaneous acquisition of the imprint of multiple fingers is therefore hardly achievable.

Various devices for displaying information using LC cells (LCD, LC display) are described in US2018/0357460a 1. According to fig. 16c, 16d of US2018/0357460a1, a grid-shaped arrangement of point light sources (e.g. micro LEDs) emitting directional scanning light is used for illumination to collect finger prints in case of an LC display. The point light sources are arranged in front of a background illumination device emitting diffuse light. The optical sensor is arranged above the illumination means, because the usual backlighting means of an LC display are opaque on the side thereof facing away from the pixels of the LC cell. The detector is here integrated in the rear plane (back plate) of the LC cell. In order not to completely block the light of the background illumination means, the point light sources for generating directional light are arranged in a distance from each other which is, for example, larger than the pixel width and height corresponding to the LC cell. Nevertheless, in order to achieve illumination that is as uniform as possible, light blocking elements are arranged in the regions between the point light sources, which light blocking elements block light from the background illumination device, whereby the brightness is disadvantageously reduced although the uniformity of the illumination is increased (when the point light sources are switched off). Furthermore, when using illumination in the form of point light, it may be necessary for accuracy reasons to collect the skin imprints segment by segment and then combine them into the whole imprint. The light source for the illumination in the form of a spot light can also be arranged above the optical sensor element, wherein the optical sensor element is in any case arranged above the background illumination of the LC cell.

In US10177194B2 a device for displaying information with OLEDs and for capturing individual finger prints on the basis of contact is described, wherein an additional illumination device for emitting directional light is arranged below the non-transparent OLED pixels, wherein the light is emitted into the regions between the OLED pixels; therefore, in principle, not the entire possible area is used for light emission, and the luminance is lowered. The sensor element is also arranged below the OLED pixel, but above the additional illumination means. Being an OLED, no backlighting is required. In the assembly described in US10177194B2, only a maximum of approximately 10% of the directed light emitted by the additional lighting means reaches the sensor element for design reasons, so that a loss of accuracy can occur here. The light guiding structure is used to generate directional illumination. In order to couple out directional light from the light guide, in US10177194B2 the light of the additional illumination means is coupled into the transparent substrate layer and from there into a light guiding structure, which is arranged below and connected with the transparent substrate layer. The light-conducting structures in turn have a large number of optical microstructures, for example microprisms, which serve as coupling-out elements and deflect the light in the direction of the placement surface for the finger.

In summary, the devices presented in the prior art have the disadvantage that, for an additional illumination layer arranged above the display unit for displaying information, the sharpness and brightness of the displayed information is reduced, although the additional illumination device is not activated. For an activated additional lighting device, the additional lighting device may also illuminate the displayed information more as long as the additional lighting device is located in the visible range. Although the prior art also describes assemblies in which an additional illumination device for generating directional light for finger print acquisition is arranged below the LC cell or OLED cell, here high transmission losses may occur which may affect the quality of the finger print acquisition. Although this can be compensated for with a stronger light source, this ultimately leads to higher energy consumption and is therefore particularly disadvantageous for mobile, battery-powered devices.

Disclosure of Invention

The object of the invention is therefore to develop an assembly with which it is possible to capture imprints of skin regions of a plurality of limbs simultaneously with high quality on the entire surface of a display screen of a mobile device without impairing the clarity of the display screen, wherein the assembly also operates as energy-efficiently as possible. It is also an object to achieve a method that is as energy-efficient as possible in order to capture imprints of skin areas of a plurality of limbs on such a device.

This object is achieved by a device for displaying information by reflection and for simultaneously recording an imprint of a plurality of blood-circulating skin areas of a limb of a person upon contact, the device having the following features:

the device initially comprises a placement surface for placing the limb, seen in the direction of the skin area in contact. The mounting surface is usually made of glass, but may also be the boundary surface of a protective film (for example made of plastic) applied to the glass. Always seen from the direction of the skin area in contact, the touch-sensitive layer is arranged below the placing surface, the touch-sensitive layer registering whether the skin area is placed on the placing surface. Such touch sensitive layers are known in the art and are connected to the control means of the device, for example in a mobile device. Furthermore, in the present invention, the touch sensitive layer is also used to activate or deactivate the sensing technology used to capture the skin print.

The LC cell (liquid crystal cell) is arranged below the touch sensitive layer. The LC cell comprises pixels arranged in a grid, which pixels are typically composed of red, green and blue sub-pixels, wherein the color definition is performed by means of respective color filters; the pixels or sub-pixels can be individually controllable by means of the control unit. The term LC cell here refers exclusively to pixel structures which can be switched to transmissive or opaque, but not to their background illumination means, wherein the polarizing structures above and below the pixels, which are usually required for changing the transmission properties, are also counted as LC cells, as are the polarizing structures arranged above the pixels and the color filters between the pixels. It is important that no additional layers (for example structured light-conducting layers or translucent sensor layers) which could reduce the brightness or the sharpness of the display screen are arranged above the LC cell, apart from the mentioned layers (placement surface, protective layer if appropriate, touch-sensitive layer). Between the polarizing structure under the pixel and the pixel itself, a so-called partially transparent "backplane" is arranged, via which the pixel is controlled. The back plate may be provided with an absorbing layer at the lower side of its non-transparent area to avoid reflection of light emitted by the lighting unit described below in the direction of the placing surface.

A lighting unit having a transparent light guiding layer body and first and second lighting devices is arranged below the LC unit. The first illumination device is here configured to illuminate the LC cell with diffused light in a first wavelength range, that is, light of the first wavelength range incident into the light guiding layer body is diffused upward toward the placement surface. The first illumination device thus achieves background illumination for the LC cell.

The second illumination device is configured to emit directional light over a limited angular range of no more than 20 around a predetermined central angle (i.e. +/-10 around the central angle), the second illumination device emitting light in a second wavelength range. The two wavelength ranges may be coincident, partially overlapping, or completely different from each other. In particular, each wavelength range may also comprise only a single wavelength within a tolerance (e.g. a tolerance predetermined by the filter). The central angle is predetermined in such a way that light which is emitted within a limited angular range and is deflected by the LC cell and the touch-sensitive layer on the bottom side of the placement surface is at least partially reflected, for example predominantly totally reflected, on the placement surface (with the medium attached thereto) with a refractive index which deviates from the refractive index of the material of the placement surface. The medium may be air, for example.

The central angle does not necessarily enclose 0 ° with the surface normal of the placement surface, but preferably encloses an angle of between 0 ° and 80 °, particularly preferably between 0 ° and 70 °, with the surface normal. Particularly preferably, the limited angular range also only includes angles around the central angle of not more than 10 °, so that the papillary structures and here also the details can be imaged as clearly as possible on the optical sensor (which will be described below).

Here, both variants are particularly preferred. In the case of a total reflection principle which is to be disturbed for reflection, the central angle is preferably greater than the critical angle for total reflection, for example 42 ° in the case of a normal glass-air transition. In this way, the reflection at the boundary surface is particularly strong, the light is used efficiently, and the contrast is correspondingly high. Particularly preferably, the angles of the limited angular range around the central angle are such that they are larger than the critical angle for total reflection. In another case, if total reflection is not used, but normal reflection is used, the central angle is preferably 0 °, in order to keep the optical path between the reflection on the mounting or boundary surface and the detection on the sensor layer as short as possible and thus the resolution as high as possible. In this case, the light quantity is significantly lower, because generally not more than 4% of the light is reflected on the placed face as a boundary face with the air.

Diffuse illumination alone is not suitable for imaging skin marks, since the distance between a sensor layer, which is described later, arranged below the light-guiding layer body and the placement surface can reach several 100 μm, so that papillary structures and details of the skin (e.g. pores) cannot be resolved by the sensor element. This loss of detail, which otherwise may be in a size arrangement of only 50 μm, is caused by the wide-angle spectrum of the diffuse illumination device, which can cause the structures to be imaged to blur with increasing distance unless no imaging or collimating optics are used. On the other hand, when the display screen is used for displaying information, a diffuse illumination device is necessary to illuminate the display screen as uniformly as possible.

The pixels of the LC cell can here be switched between a state transparent to diffuse light and directed light and a state at least opaque to diffuse light by changing the polarization direction of the light which has been linearly polarized upon entering the LC cell. As above, the pixels of the LC cell are illuminated by the diffuse light emitted by the first illumination means to display the information provided for display by means of the drive unit. Switching to a state that is also opaque to the directed light is not absolutely necessary, but is alternatively possible.

Finally, an optical sensor layer with sensor elements arranged in a grid pattern is arranged below the light-conducting layer body, the sensor elements being sensitive to at least light of a second wavelength range.

In contrast to the prior art, the optical sensor layer is therefore arranged below the illumination unit. Since the sensor element is arranged below the light guiding layer body, this light guiding layer body has to be transparent, unlike the prior art, where the backlighting arrangement for the LC cell is designed to be opaque, since it has a highly reflective layer on its bottom side, which maximizes the efficiency in the light output. In order to increase the light output efficiency of the diffuse illumination means in the device according to the invention, the sensor layer, which is usually metallic, or at least the surface of the sensor element, can be designed to be partially reflective, except for the opening of the element detecting light of the second wavelength range.

Due to the fact that the sensor layer forms the lowest layer of the device, the one or more sensor elements do not have to be designed to be transparent or translucent, so that cheaper components, such as CMOS based sensors, can be used here. Since all components required for the skin print registration are arranged below the LC cell, the display screen is not visually disturbed. Since neither diffuse nor directed light has to pass through the region with the translucent sensor (the transmission of which is typically only 1% to a maximum of 30% of the incident light), the energy efficiency can be increased, requiring less energy for the same brightness in e.g. conventional devices.

In a further embodiment, the directed light is not changed in its polarization direction by the LC layer in certain central angles, so that the directed light can always pass through the LC cell unimpeded, whether the LC cell switches to the opaque state or the transparent state. The reason for this is that some LC cells may have a strong angular and wavelength dependence in their transmission characteristics, which results in directional light passing through the LC cell regardless of the switching state. For this reason, the central angle of the directed light should be between 30 ° and 80 °, preferably between 40 ° and 70 °, and particularly preferably between 50 ° and 70 °. In this embodiment, an LC cell with non-crossed linear polarizers (i.e., parallel oriented polarization filters) must be used, otherwise the oriented light will be extinguished.

However, when illuminating with directional light on an LC cell, if the light used is unpolarized, a loss of about 50% still occurs due to polarization on the lower polarization structure. Such losses can be avoided by using, for example, a laser or other light source emitting polarized light as the light source for the directional illumination.

Furthermore, in some embodiments, if the central angle is set to a region above the critical angle of total reflection on the placement surface, information may also be displayed using the second illumination device. This may be achieved, for example, by selecting a suitable inclination angle of, for example, a prismatic out-coupling structure, which is correspondingly large to impart a large change of direction to the light guided in the light guide when impinging on a suitable inclined surface of the out-coupling structure. Furthermore, this depends on the refractive index difference of the refractive index between the light guide body and the adhesive layer surrounding the light guide body, the refractive index of the adhesive layer being lower than the refractive index of the light guide body, since it is thereby defined which light angles are mainly guided.

To save energy, the first illumination means may be switched off when skin prints of the limb are taken. Instead, the second illumination means must be activated only when one or more skin areas are to be detected; the second lighting device may be integrated into the control device of the respective application, for example. Access to the second illumination means may here be locally limited to those areas of the touch sensitive layer where placement of one or more skin areas has been detected, for example to a bar-shaped area in case of illumination from the side.

In a particularly preferred embodiment, the first wavelength range for diffuse illumination and the second wavelength range for directional illumination do not have an intersection, i.e. the ranges do not overlap each other. In this way, the overlap of the signals of the two lighting devices can be minimized. Preferably, the first wavelength range then comprises visible light and the second wavelength range comprises invisible light, preferably in the NIR range between 780nm and 3000nm, wherein illumination in the UV-a range between 315nm and 380nm is also possible.

Alternatively, the second illumination device may also be designed to emit monochromatic light, i.e. the second illumination device emits light only in a very narrow band. In this case, in order to separate the light of the second illumination device from the light of the first illumination device, a transmission filter is arranged between the optical sensor layer and the light guide body to preferably pass only the light of the second illumination device.

Here, the basic components of the assembly are the light guiding layer body and the lighting device. The light guide layer body may be implemented in various ways. In a first design, the light guiding layer body includes a lower transparent layer as part of the first illumination device and an upper transparent layer as part of the second illumination device. The two layers are preferably designed substantially plate-shaped, i.e. have two large faces (also referred to as main faces or large side faces) which are arranged substantially parallel at a small distance from one another. The two large faces are connected at the edges by narrow sides, which form the edges of the panel. The geometry of the panel is here usually rectangular, but this is not mandatory. The first illumination device comprises a first light source emitting light in a first wavelength range and the second illumination device comprises a second light source emitting light in a second wavelength range. Light of the first light source is coupled into the lower transparent layer and light of the second light source is coupled into the upper transparent layer. Preferably, the first and second light sources are each arranged on a narrow side of the respective plate-shaped layer, and the light can then be coupled into the respective layer laterally via the narrow sides or also via corners of the light-guiding layer (which is preferably shortened or provided with chamfers for this purpose). When light coupling is performed from the side, in particular for the second light source for generating directional light, but also for the first light source, it is advantageous if the light sources each consist of a large number of individual light sources, wherein the emission angle of each individual light source is preferably limited by a collimating means, for example an absorbing cylindrical structure and/or an optical lens. Thereby increasing the maximum available brightness. Such spatial collimation is particularly advantageous, in particular for generating directional light, since the angle of incidence of light falling on the light guide may from the outset already be limited to a small angular range depending on the specific collimation structure. Optical coupling for diffuse illumination from below is also possible if the first light source is, for example, integrated into the optical sensor layer and, for example, arranged between the sensor elements.

Both the light of the first light source and the light of the second light source are guided in the individual layers of the light-guiding layer body by means of Total Internal Reflection (TIR), the angle of incidence range (angle of incidence range having an angle in which the light of the first or second light source falls laterally on the boundary surfaces of the individual layers) having to be selected accordingly in such a way that the light is also guided by total reflection at the critical angle of the angle of incidence range. Here, an optical layer having a lower refractive index than the respective layers of the light guide body is applied onto the large face. For example, these optical low-refractive layers may be composed of air or a transparent adhesive. The transparent layer of the light guide has a boundary surface on its main surface, and a first out-coupling structure for out-coupling of diffuse light is formed on the boundary surface of the lower transparent layer, and a second out-coupling structure for out-coupling of directional light is formed on the boundary surface of the upper transparent layer, wherein light is out-coupled in either case in the direction of the placement surface.

In principle, it is also possible to exchange the stacking order of the transparent layers and the respective illumination device or light source and to construct a out-coupling structure on the boundary surface of the lower transparent layer for out-coupling the directional light and a out-coupling structure on the boundary surface of the upper transparent layer for out-coupling the diffuse light, even if this would lead to a further widening of the emission angle of the directional light, that is to say a limited angular range which is much narrower than in the first case (in which the widening of the guided-back light occurs before impinging on the sensor) should be selected accordingly.

The first light source and the second light source can be designed such that the light is coupled into the lower transparent layer or the upper transparent layer laterally, and the first and second light sources are combined to form a common edge lighting. In an extreme case, the first and second light sources are combined to form a single light source, the light of which is coupled into the light guiding layer body via the edge. Since here the diffuse illumination and the directed illumination are performed using light of the same wavelength, it is expedient to arrange an additional diaphragm layer between the optical sensor layer and the light-guiding layer body for spatial angle selection, so that the sensor elements of the optical sensor layer can essentially predominantly or exclusively receive the light of the directed illumination.

The coupling-out structure of the directed light and the diffuse light is designed such that the illumination per unit area in terms of intensity and also in terms of its angular distribution for the directed light takes place predominantly uniformly, irrespective of whether the skin part of the limb rests on the placement surface at one or more points.

This is achieved by a correspondingly selected distribution of the coupling-out structures over a large area. For example, the number of out-coupling structures may increase with increasing distance from either side of where the light is coupled.

In an alternative design of the device, the lower and upper transparent layers are not used in the light guiding layer body, but the light guiding layer body comprises a single transparent combined layer of transparent, substantially plate-shaped design. The first illumination means comprises a first light source and the second illumination means comprises a second light source, wherein the light of the first light source is preferably coupled into the combination layer on a first narrow side, preferably laterally or laterally from a corner, and the light of the second light source is preferably coupled into the combination layer on a second narrow side opposite the first narrow side, preferably laterally or laterally from a corner, or from below by means of an additional optical element (for example a lens or a prism arranged transversely to the sensor layer). Here, the light is also guided by means of total internal reflection, and a combined outcoupling structure for simultaneously outcoupling diffuse light and directional light in the direction of the placement surface as a function of the direction of incidence (for example from the first or second narrow side) is preferably formed on the boundary surface of the transparent combined layer. In addition or alternatively, the first and second coupling-out structures can also be arranged here in order to increase or ensure homogeneity, for example on the boundary surface opposite the combined coupling-out structure. It is particularly important here that the stray light is coupled out as uniformly as possible. The means for homogenizing the directed light, which is unimportant to a viewer of the display screen since no information is to be displayed therewith, can also be integrated into the optical sensor layer in such a way that, for example, the diaphragm size is adjusted there or the sensitivity of the sensor element is increased gradually with increasing distance from the side on which the light is coupled, or a translucent layer is applied with decreasing absorption from this side.

The invention also relates to a method for simultaneously acquiring skin imprints of a plurality of limbs placed on a placement surface, in particular with a device as described above. Viewed from the direction of the limb, the device comprises: placing the noodles; a touch sensitive layer; an LC cell having individually controllable pixels arranged in a grid; a lighting unit having a transparent light guide layer body; a first illumination device for illuminating the LC cell with diffuse light in a first wavelength range; a second illumination device for emitting directional light in a second wavelength range; and an optical sensor layer having sensor elements arranged in a grid-like manner that are sensitive to light of a second wavelength range.

In the method, an LC cell of an apparatus (e.g. a mobile phone or a tablet computer) is during its operation first illuminated with diffuse light in a first wavelength range by means of a first illumination means, wherein pixels of the LC cell are switchable between a state transparent to the diffuse light and a state opaque. In this way, information may be displayed. This is the usual mode of operation of such a display screen or tablet computer when no finger is placed. Information is displayed in color because each pixel is typically composed of a plurality of sub-pixels that emit light in the primary colors red, green, and blue.

The touch-sensitive layer detects whether an area of skin is placed on the resting surface. In the case of a skin region being placed, the sensor elements of the optical sensor layer are activated so that they can detect light, and furthermore the second illumination means is switched on, which is switched off in the normal operating mode (in which only information is displayed). If a touch-sensitive layer is present, the corresponding information (e.g. whether to place one finger or a plurality of fingers) is automatically available, wherein the touch-sensitive layer also registers the place of placement on the two-dimensional placement surface. The user-directed information relating to the captured imprint may be displayed simultaneously on the display screen of the device.

After the second illumination means has been switched on, it emits directional light within a limited angular range of not more than 20 ° around a predetermined central angle, wherein the central angle is predetermined in such a way that the light emitted within the limited angular range and deflected by the LC cell and the touch-sensitive layer on the bottom side of the mounting surface is predominantly totally reflected on the mounting surface (with the medium attached thereto) with the refractive index of air. However, light may then pass through the placement surface, particularly when placed against the skin prominence of a finger or other extremity. The light reflected from the placement surface is then detected by means of the optical sensor layer. Due to the arrangement of the sensor elements in a grid, the detected light may be collected or registered as an imprint of one or more limbs, i.e. the intensity values detected by the optical sensor elements are calculated as one or more imprints, using image processing methods known in the art. If the registration or acquisition of the skin area of the limb is successfully completed or aborted, for example because the finger is removed from the underlying surface before the acquisition is completed, the optical sensor layer is deactivated and the second illumination means is switched off.

Since the second illumination means and the optical sensor element consume energy only when a finger is placed, the method operates in an energy efficient manner. Furthermore, the switching on of the second illumination means and the optical sensor element may also be connected to other conditions, for example the switching on may be limited to applications that specifically require testing of finger prints, such as online banking applications.

In a final step, the acquired one or more imprints are compared with imprints stored in a database, and, depending on the result of the comparison, one or more actions are performed, if necessary. For example, a mobile device may be assigned to multiple users in a company, where each user has its own user profile and its own user interface. The finger print can then be used to load a specific configuration file of the user interface for the user.

Preferably, for added safety, a single acquisition is performed for each limb placed. The acquisition may also be repeated if a change in position of one or more limbs is detected or if additional limbs are placed. Also for a more energy-efficient design of the method, the detection of light of the second wavelength range may be limited to the area where the placement of the limb is detected by the touch sensitive layer.

A possible application of the invention is mainly the integration of multi-finger print sensing technology in LC display screens. For example, these LC displays may be part of smart phones, tablets, televisions, laptops and other devices with displays on which user authentication is to be performed. One example of an application is a touch sensitive display screen in a car, which is a virtual dashboard and thereon a virtual start button, which can be turned on and start the car upon recognition of a respective finger mark of a registered user, and/or a virtual switch by means of which a user-specific seat and mirror combination is set.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone without departing from the scope of the invention.

Drawings

The invention is explained in more detail below on the basis of embodiments with reference to the drawings, which also disclose features essential to the invention. These examples are for illustration only and should not be construed as limiting. For example, a description of an embodiment with multiple elements or components should not be construed as implying that all such elements or components are necessary for an implementation. Rather, other embodiments may include alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different embodiments may be combined with each other, unless otherwise indicated. Modifications and variations described for one of the embodiments may also be applicable to the other embodiments. To avoid repetition, elements that are the same or correspond to each other in different figures are denoted by the same reference numerals and will not be explained again. The attached drawings are as follows:

figures 1a, b show two cross-sectional views of a device for displaying information and for simultaneously acquiring skin prints of a limb upon contact in the case of finger placement,

figure 2 shows a cross-section of a light guiding layer body having two transparent layers,

figure 3 shows a cross-section of a light guiding layer body in an alternative design,

4a) to c) show different possibilities for coupling light into the transparent layer of the light guiding layer body,

figure 5 shows another possibility of illumination of the transparent layer of the light-guiding layer body,

figure 6 shows a possible arrangement of the out-coupling elements in a top view,

FIG. 7 shows a possible configuration of an LC cell, an

Fig. 8 shows the basic procedure of a method for simultaneous acquisition of skin imprints of multiple limbs.

Detailed Description

Fig. 1a first shows a cross section of a device for displaying information and for simultaneously taking imprints of a plurality of blood-circulating skin areas of a limb of a person upon contact. The finger 1 here serves as an appendage, for example. Viewed in the direction of the skin area in contact, the device comprises first: a placing surface 2 for placing limbs. In this example, this is part of an optional protective layer 3, which protective layer 3 serves to protect the underlying components. For example, it may be a glass or plastic layer. A touch-sensitive layer 4 is arranged below the optional protective layer 3, the touch-sensitive layer 4 registering whether a skin area has been placed on the placement surface 2. Below the touch sensitive layer 4 is arranged an LC cell 5 with pixels 6 arranged in a grid-like manner, the pixels 6 being individually controllable by means of a control unit (not shown). Below the LC cell 5, a lighting unit with a transparent light guiding layer body 7 and a first and a second lighting device is arranged, which will be described in more detail with reference to fig. 2 and 3. Finally, an optical sensor layer 8 is arranged below the light-conducting layer body 7, the optical sensor layer 8 having sensor elements 9 arranged in a grid pattern.

The construction of the lighting unit is explained in more detail below on the basis of an alternative design according to fig. 2 and 3. The illumination unit includes a transparent light guide layer body 7 and first and second illumination devices. The first illumination device is configured to illuminate the LC cell with diffuse light in a first wavelength range. In another aspect, the second illumination device is configured to emit directional light within a limited angular range of no more than 20 ° about the predetermined central angle and within a second wavelength range. The central angle is predetermined in such a way that light which is emitted within a limited angular range and is deflected by the LC cell 5 and the touch-sensitive layer 4 on the underside of the placement surface is at least partially reflected on the placement surface (with the medium attached thereto) with a refractive index which deviates from the refractive index of the material of the placement surface (2). The pixels 6 of the LC cell 5 can be switched between a state transparent to diffuse light and directed light and a state at least opaque to diffuse light. For displaying information the pixels 6 are illuminated by diffuse light. On the other hand, the sensor elements 9 of the optical sensor layer 8 are sensitive only to light of the second wavelength range of the directional light, but it is not excluded therein that the second and second wavelength ranges overlap or that the second wavelength range is comprised in the first wavelength range. The surface of the sensor element 9 facing the light guiding layer body 7 may be designed to be reflective to increase the light output of the diffused light and with a diaphragm structure to improve the angular selectivity and/or uniformity of the directed illumination. The central angle encloses an angle of between 0 ° and 80 °, preferably between 0 ° and 70 °, with the surface normal of the placement surface 2. The limited angular range preferably comprises an angle of not more than 10 ° around the central angle, i.e. +/-5 ° around the central angle.

On the other hand, if the first and second wavelength ranges overlap, the second illumination device may be designed in such a way that it emits monochromatic light, preferably in a very narrow wavelength range of a few nanometers. Then, in order to separate the light of the second illumination device from the light from the first illumination device, a transmission filter is preferably arranged between the optical sensor layer 8 and the light guide body 7.

Fig. 2 shows a first embodiment of the light-guiding layer body 7 with the first and second lighting means. Here, the light guide layer body 7 has a lower layer 10 and an upper layer 11. The lower layer 10 and the upper layer 11 are both made of a transparent material (e.g. glass, PMMA or polycarbonate) and are substantially plate-shaped. The lower layer 10 is assigned to a first lighting device and the upper layer 11 is assigned to a second lighting device. Thus, the lower layer 10 is used to illuminate the LC cell 5 with diffuse light in the first wavelength range, while the upper layer 11 is used to emit directional light as described above. The first lighting device comprises a first light source 12 and the second lighting device comprises a second light source 13. The first light source 12 and the second light source 13 are only symbolically shown in fig. 2 and 3; possible embodiments are shown in fig. 4 and 5. The light of the first light source 12 is coupled into the lower transparent layer 10, for example laterally, laterally from the corners or from below. The light of the second light source 13 is coupled into the upper transparent layer 11 laterally at the narrow sides or laterally from the corners or from below. In the lower and upper transparent layers 10, 11, respectively, the light is guided by total internal reflection, so that the light cannot be coupled out of the light guide without auxiliary devices. These auxiliary devices are formed at the boundary surface of the lower transparent layer 10 by the first out-coupling structures 14 and at the boundary surface of the upper transparent layer 11 by the second out-coupling structures 15, wherein the boundary surfaces mean the large or major surfaces of the respective transparent layers 10, 11, and the out- coupling structures 14, 15 may be arranged at one or both boundary surfaces of the respective layers. In the present case, the first out-coupling structure 14 is configured at the lower boundary surface as a concave recess in the lower transparent layer 10. Alternatively or additionally, convex elevations may also be formed at the upper boundary surface of the lower transparent layer 10. If light from the first light source 12, which is incident in the lower transparent layer 10, impinges on the first out-coupling structures 14, the light (indicated by small arrows) is substantially diffusely deflected and out-coupled. Optionally, a reflective layer 101 may be applied on a narrow side of the lower transparent layer 10, opposite to the narrow side used for light coupling, to improve the light output of the diffuse illumination. On the other hand, the second coupling-out structure 15 is formed here on an upper boundary surface of an upper layer, which has, for example, a rectangular base and a prismatic longitudinal section, wherein the coupling-out structure 15 can also be arranged alternatively or additionally on a lower boundary surface of the upper layer 11 and can also be configured in the form of a cuboid. The light outcoupling therefore takes place here only in a narrow angular range predetermined by the geometry, in particular by the inclination angle of the prism surface or the inclined surface of the outcoupling structure, wherein the inclination angle is preferably 5 ° to 25 °, particularly preferably 10 ° to 20 °, relative to the large surface of the transparent layer 11. The directional light coupled out by the second out-coupling structure 15 and the diffuse light coupled out by the first out-coupling structure 14 are both coupled out in the direction of the mounting surface 2. In order to guide the light in the lower transparent layer 1(2) and the upper transparent layer 11, respectively, by means of total internal reflection, a separating layer 16 is arranged at the boundary surface, respectively. Here, this may be, for example, air or an adhesive layer, but other materials having a correspondingly lower refractive index than the transparent layers 10, 11 are also conceivable, which allow total internal reflection within the transparent layers 10, 11, wherein the refractive index of the separating layer 16 is, for example, 1% to 30%, preferably 5% to 30%, more preferably 10% to 25%, lower than the refractive index of the transparent layers 10, 11. The isolation layer 16 here also fills the concave recess of the first out-coupling structure 14, for example. In particular, optically clear double-sided adhesive tapes (OCA) or liquid adhesives (LOCA) which cure under heat or UV radiation are also suitable as materials for the separating layer. It is possible here to use, for example, siloxanes, acrylates or epoxides whose refractive index is between 1.2 and 1.5, preferably between 1.3 and 1.47, and particularly preferably between 1.35 and 1.43. The material for the transparent layers 10, 11 (e.g. glass, PMMA or polycarbonate etc.) is chosen to have a refractive index between 1.4 and 1.8, preferably between 1.45 and 1.6, and particularly preferably between 1.47 and 1.55.

Fig. 1b shows a design of the light-guiding layer body 7 that is optically coupled into at least one of the two transparent layers from below, wherein in the example shown in fig. 1b the light of the second light source 13 is coupled into the upper transparent layer 11 and/or the light of the first light source 12 is coupled into the lower transparent layer 10. For this purpose, an overhang 71 of the lower transparent layer 10 is formed on the light guide layer body 7, here facing to the left. Likewise, an overhang (not shown here) of the upper transparent layer 11 can also be formed on the right side in order to couple the light of the light source 13 into the upper transparent layer 11 from below. A prism-shaped coupling-in element 72 or a lens-shaped coupling-in element 73 is then mounted, for example, on the bottom side of the overhang 71 for optical coupling. In order to connect these elements to the light guiding layer body 7 or the transparent layers 11, 12, it is preferable to use an adhesive that is matched in refractive index, the adhesive also having as much as possible the same refractive index as the transparent layers 11, 12 and the incoupling elements 72, 73. In this way, the overall construction of the device can be designed more compactly, since it can also be coupled into very thin transparent layers 11, 12.

In the embodiment shown in fig. 1b, a transmission filter layer 81 is also arranged between the sensor layer 8 and the light-conducting layer body 7, which transmission filter layer 81 can be designed, for example, as a bandpass filter and is substantially transparent only to the light of the second light source 13. This is advantageous when the first and second wavelength ranges overlap.

In fig. 2, the first light source 12 and the second light source 13 are shown separately, but there is also the possibility of combining the first light source 12 and the second light source 13 to form a common edge lighting device in the case of lateral coupling, wherein then preferably a diaphragm is arranged on the sensor element 9 for angle selection, so that the sensor element 9 preferably detects the directed light of the second light source after reflection on the placement surface. In this case, the first illumination device will always be on regardless of whether or not the finger print is registered.

In the case of two separate light sources 12, 13, it is also advantageous to use an adapted transmission filter in the form of a transmission filter layer 81 (e.g. a band pass filter) between the optical sensor layer 8 and the lower transparent layer 10, the transmission filter preferably being transparent only for light of the second light source 13 within a narrow range of bandwidths of e.g. 5nm or 10nm to 200nm, preferably 10nm to 100nm, particularly preferably 10nm to 50 nm. Thereby, the light to be detected by the optical sensor element 9 is spectrally limited to a narrow range of several nanometers. The narrower the spectral range, the less the interference light from the first light source 12 is detected by the optical sensor element 9, but the amount of light that can be detected as a whole is also reduced, thereby decreasing the light efficiency. A corresponding compromise must be found here which is suitable for the application, if the filter is not too narrow, this being achieved by the transmission filter layer 81. The reduction in light efficiency can be offset with a monochromatic light source, and a transmission filter layer 81 having a narrower bandwidth of less than 5nm can be used accordingly.

A particularly preferred alternative embodiment is shown in fig. 3; the light-guiding layer body 7 can be made thinner here, which reduces the constructional depth of the device. In this case, the light-conducting layer body 7 comprises a transparent, essentially plate-shaped designed combination layer 17, which combination layer 17 is also referred to as a single layer. The combined layer 17 is the only layer of the light guiding layer body 7, except for the separation layer 16. Here, the first lighting device also comprises a first light source 12 and the second lighting device comprises a second light source 13. The light of the first light source 12 is here preferably coupled into the combination layer 17 laterally or laterally from a corner on the first narrow side 18. The light of the second light source 13 is preferably coupled into the combination layer 17 laterally or laterally from a corner on a second narrow side 19 opposite the first narrow side 18. Here, in the case of a plate-shaped light guide, those sides or edges connecting the large faces or major faces to each other are referred to as narrow sides. The light is also guided within the combination layer 17 by means of total internal reflection, wherein a combined coupling-out structure 20 for coupling out diffuse light and directional light in the direction of the placement surface 2 as a function of the direction of incidence is formed on the boundary surface of the transparent combination layer 17. If, like in the embodiment of fig. 1a, an overhang is constructed on both sides, it is also possible to couple light into the combined layer 17 from below.

The combination outcoupling structures 20 are designed here such that, when the light from the first light source 12 (illustrated by solid arrows) is illuminated from the left in fig. 3, i.e. from the narrow side 18, the light is coupled out non-directionally, i.e. diffusely, in the direction of the placement surface 2. The respective portion of the combined out-coupling structure 20 is here illustratively constructed with a uniform or variable curvature/curvature for out-coupling diffuse, non-directional illumination. Light incident from the opposite side (originating from the second light source 13 and represented here by a dashed arrow) is deflected from the right in fig. 3 directionally towards the mounting face 2 when hitting the combined outcoupling structure 20. At this time, the combined out-coupling structure 20 has a flat surface, which however has a prismatic form of inclination compared to the placement surface 2, i.e. encloses an angle with the placement surface 2 that is not zero. Depending on the inclination, the directional light is coupled out around a defined central angle in the direction of the placement surface.

In addition to the overall construction height of this embodiment being small, fewer layers must be interconnected. The smaller distance from the contact surface also allows a higher quality image of the captured skin print. For light sources which are incident from only one side (in the embodiment shown in fig. 2, it is in principle also possible to arrange the first and second light sources 12, 13 on both sides, in contrast to the embodiment of fig. 3), a uniform intensity distribution can be achieved by the number and distribution of the coupling-out structures 14, 15 on the boundary surface, which is possible in the case of the use of the combined coupling-out structure 20 either only for diffuse light or only for directional light, since the same spatial distribution of the coupling-out structures is used for both. In general, by combining the distribution of the out-coupling structures 20 it will be ensured that the intensity of the diffusely outcoupled light appears substantially homogeneous, since this is the light that is predominantly perceived by the viewer. In this case, the light coupled out from the other side for the directional illumination is largely coupled out in the vicinity of the region of incidence, since there are a large number of combined out-coupling structures 20. Homogenization at least for the detection of the directed light can then advantageously be achieved by an additional diaphragm above the individual sensor elements 9, the sensor elements 9 having a smaller opening in the region of the coupling of the light of the second light source 13 than on the opposite side to the side of the first light source 12 on which the light is coupled. The transmission may also vary continuously with thicker or thinner transmission layers, as described for example in DE102017119983B3, the disclosure of which is incorporated herein.

As indicated by the arrows in fig. 3, the light is preferably already coupled into the light guide at an angle on both sides, the light guide fulfilling the requirements for total internal reflection, thereby achieving a higher light utilization efficiency. This may be achieved, for example, by arranging the light source obliquely on the light guide or by upstream coupling optics.

With respect to the incidence of light, the simplest method is to couple light from the side (as shown by way of example in fig. 3). However, in order to achieve the highest possible resolution of the biometric features of the finger placed on the placement surface, it is advantageous to couple light into the respective layer via the corners. This will be explained in more detail with reference to fig. 4. In fig. 4a) to c), three embodiments of a lighting unit are shown, which has a light-conducting layer body and a lighting device for corner light coupling-in. The figure is a plan view of the main surface of the transparent layer 10, 11 or 17 of the light guide, respectively. Fig. 4a) shows an embodiment of light incoupling, in which the first or second light source is designed as an LED (the same type of light incoupling applies to directional light and diffuse light), and in which the light incoupling is carried out on at least one surface formed by shortening the corners of the respective transparent layer of the light-guiding layer body. Such a shortened corner 21 results in an additional narrow side (Schmalseite) which encloses an angle of, for example, 135 ° with the narrow side of the usually present rectangular plate-shaped layer. In this case, there is no need to pre-collimate the light emitted by the light sources 12, 13 in the horizontal direction. In order to avoid reflections and the associated formation of a double image of the finger print, it is then advantageous to provide an absorption coating on the other narrow side of the light-conducting layer (to which no light is coupled), which absorption coating absorbs the light arriving there or couples it out laterally, so that this light no longer reaches the placement surface.

In fig. 4b) and c) further additional measures are shown in comparison with fig. 4a), wherein in fig. 4b) the light distribution or light homogenization is improved by means of a diffusion disk 22, whereby the light is emitted uniformly in all directions, while in fig. 4c) the shortened corners 21 are designed as concave arcs, so that all light beams emitted divergently from the first light source 12 or the second light source 13 can enter the light-guiding layer without interruption, whereby light emitted only from a single LED can also propagate and be coupled out in the entire transparent layer 10, 11 or 17.

Fig. 5 shows a further embodiment for coupling light at the narrow side, which is particularly suitable for generating directional light. The first light source 12 or the second light source 13 is here composed of a number of individual LEDs 23, the LEDs 23 being arranged along the narrow side for coupling. The LEDs 23 are here embedded in a cylindrical or truncated-cone-shaped absorption structure 24 (shown here in cross section). The absorbing structure 24 ensures that the light emitted by the LED is spatially collimated up to an angular range of, for example, 10 ° around the axis 25. The usable angle range depends in particular on the extent of the cylindrical or truncated-cone-shaped absorbent structure 24 in the emission direction.

Fig. 6 shows a top view of two portions of the upper transparent layer 11 with the second out-coupling structure 15. The second out-coupling structure 15 is configured as a wedge and is a rectangular or trapezoidal surface rising obliquely from the direction of illumination, as shown in the sectional view of fig. 2. Here, the upper boundary surface of the upper transparent layer 11 is shown, in which the second out-coupling structure 15 is structured. The second out-coupling structures are arranged in a plurality of rows, wherein the distance of the individual rows from each other decreases with increasing distance from the second light source 13 to improve the uniformity of the intensity of the emitted light, which is also shown in fig. 2.

Fig. 7 shows in detail a possible construction of the LC cell 5. The core of the LC cell 5 is a liquid crystal layer 27 with liquid crystal molecules 28, the liquid crystal molecules 28 being contained in a cell not shown here. The liquid crystal molecules 28 are shown here in thin stick form to depict the polarization direction and the rotation of the polarization of the light. The cell with liquid crystal molecules 28 is bounded by a vertical alignment layer 29 (here below the liquid crystal layer 27) and a horizontal alignment layer 30 (here on top of the liquid crystal layer 27). The alignment layer is, for example, a glass plate with a plurality of parallel microgrooves (each oriented either horizontally or vertically) by means of which the liquid crystal molecules 28 are mechanically oriented helically over the length of the cell. A transparent electrode 31 in the form of a layer is arranged on the outer side of the glass plate, by means of which the orientation of the liquid crystal molecules 28 can be changed when a voltage is applied. A color filter 32, a glass substrate 33, and a horizontal polarization filter 34 are also arranged on the upper side of the transparent electrode 31 above the horizontal alignment layer 30 (i.e., in the emission direction with respect to the placement surface 2), and on the glass substrate 33. In the present embodiment, an active semiconductor array, the so-called back plate 35, is arranged on the bottom side of the electrode 31 below the vertically oriented layer 29. It is an array of transistors 36, mainly Thin Film Transistors (TFTs), where each cell is assigned a transistor 36, which transistor 36 controls the electrode of the cell located above it. The LC cell is closed at the bottom by a glass substrate 33 and a vertical polarization filter 37.

For conventional display screens it is desirable to illuminate the display screen with as much light as possible of the backlighting arrangement, which is why reflections on metal structures in the back plate 35, such as conductor tracks, do not cause interference, since the reflected light can be deflected towards the LC cell by other reflections if necessary. In this case, however, the reflection of the diffuse or directional light coupled out from the underlying light guide is undesirable, since this light reaches the sensor layer 8 directly without striking the placement surface 2 beforehand. The reflected light thus has a negative effect on the detection of the directed light by the sensor element 9, since this light represents a shift without imprinted image information. This offset can cause the photosensitive elements of the sensor layer to have saturated due to back reflection only on the backplane structure, making it difficult to detect finger lines. In the embodiment described here, the absorption layer 38 is therefore arranged below the back plate, the absorption layer 38 also being structured in an array-like manner in the structure and corresponding to the array structure of the back plate 35. The absorbing layer 38 reduces reflections on the back plate 35 and improves acquisition quality. Alternatively or additionally, a transparent back plate made of a transparent conductive material such as ITO, IZO or AZO and a transparent semiconductor such as GaN or ZnO may of course be used.

Finally, fig. 8 shows the basic procedure of a method for simultaneously capturing the imprint of a plurality of limbs placed on a placement surface 2, which can be carried out using a device, in particular as described above. Seen from the direction of the placed limb, the device comprises a placement surface 2, a touch-sensitive layer 4, LC cells 5 (with individually controllable pixels 6 arranged in a grid-like manner), illumination units (with a transparent light-guiding layer body 7 and first illumination means for illuminating the LC cells 5 with diffuse light in a first wavelength range and second illumination means for emitting directional light in a second wavelength range). An optical sensor layer 8 with sensor elements 9 arranged in a grid-like manner and sensitive to light of the second wavelength range is connected to the light-conducting layer body 7. The method can be executed on a touch-sensitive display screen of a commercially available mobile phone with a touch-sensitive display screen, a PC and the like. Typically, the information is already displayed on the display screen. The user can now place his finger 1 on the placement surface 2 at a specific point of the display screen in order to start the application, wherein the method steps described below are then performed. Another possibility for starting the method is to request security-relevant inputs in an already running application, for which the user must identify himself by finger print. In the normal state, the LC cell 5 is further illuminated with diffuse light in the first wavelength range by means of the first illumination means for displaying information, wherein the pixels 6 of the LC cell 5 can be switched between a state transparent to the diffuse light and a state opaque. If the touch-sensitive layer 4 now detects whether a finger 1 is placed on the placement surface 2, a second illumination means for emitting directional light is switched on or activated on the one hand; on the other hand, the sensor elements 9 of the optical sensor layer 8 are activated, i.e. they are able to detect incident light of a second wavelength range. Here, the detection of light of the second wavelength range may be limited to the area where the placement of the limb is detected by the touch sensitive layer 4 to save energy.

After the second illumination means are switched on, they emit directed light within a limited angular range of not more than 20 °, preferably not more than 10 °, around a predetermined central angle. The central angle is predetermined in such a way that light emitted within a limited angular range and deflected by the LC cell 5 and the touch-sensitive layer 4 on the underside of the placement surface 2 is at least partially reflected on the placement surface 2 (with the medium attached thereto) with a refractive index that deviates from the refractive index of the material of the placement surface (2). If the finger 1 is placed, directional light will be reflected at the location where the skin recess is present, because there is still an air layer between the placing surface 2 and the finger 1 at the location of the skin recess. On the other hand, at the location where the skin relief abuts against the placement surface 2, directional light enters the finger 1 through the placement surface 2 and is scattered there, so that these areas appear darker in the image. The light reflected from the placement surface 2 is detected by means of the optical sensor layer 8 and an image of an imprint of one limb or of a plurality of imprints of a plurality of limbs is acquired on the basis of the intensity difference. After completing or discontinuing the acquisition of the skin print of the limb, the optical sensor layer 8 is deactivated and the second illumination means is switched off. The acquired imprint or imprints are then compared with the imprints stored in the database 26; depending on the result of the comparison, various actions may be performed, for example, if the finger 1 is recognized, a transmission is turned on, etc.

Since the second illumination means and the optical sensor layer 8 are activated only when a finger print actually has to be registered, the method can be designed to be particularly energy efficient, so that the finger print registration or acquisition hardly affects the lifetime of the battery. The method steps may be repeated here when the limb is lifted and put in another position again, or when another limb is put in place. In this case, a single acquisition is preferably carried out for each limb placed, so that, in the case of four fingers placed, for example, ideally 4 images are generated simultaneously.

By the device and the method, for example, multi-finger authentication can be integrated into a mobile phone without affecting the quality of information display on a display screen. Almost the entire area of the device can also be used for displaying information, since the entire area of the display screen can be used for recognition of the finger print and an area only for print recognition has to be reserved. The construction is also very compact so that the constructional depth of the respective device can be kept sufficiently flat.

List of reference numerals

1 finger

2 placing surface

3 protective layer

4 touch sensitive layer

5 LC cell

6 pixels

7 light guide layer body

8 sensor layer

9 sensor element

10 lower transparent layer

11 upper transparent layer

12 first light source

13 second light source

14 first coupling-out structure

15 second coupling-out structure

16 separating layer

17 composite layer

18 first narrow side

19 second narrow side

20 combined coupling output structure

21 shortened corner

22 scattering disk

23 LED

24 absorbent structure

25 shaft

26 database

27 liquid crystal layer

28 liquid crystal molecules

29 vertically oriented layer

30 horizontally oriented layers

31 transparent electrode

32 color filter

33 glass substrate

34 horizontal polarization filter

35 back plate

36 transistor

37 vertical polarization filter

38 absorbent layer

71 overhanging part

72 prismatic coupling-in element

73 lens-shaped coupling-in element

81 transmission filter layer

101 reflective layer

Claims (17)

1. A device for displaying information and simultaneously acquiring skin imprints by means of reflection of a plurality of blood-circulating skin areas of a limb of a person on a contact-by-contact basis, comprising, seen in the direction of the contacted skin areas:

a placement surface (2) for placing the limb,

a touch sensitive layer (4), the touch sensitive layer (4) registering whether an area of skin is placed on the placing face (2),

an LC cell (5), the LC cell (5) having pixels (6) arranged in a grid-like manner which can be controlled one by means of a control unit,

-a lighting unit having a transparent light guiding layer body (7) and a first and a second lighting device, wherein

i. The first illumination means being configured for illuminating the LC cell (5) with diffuse light in a first wavelength range,

ii. The second illumination device is configured to emit directional light within a limited angular range of no more than 20 ° about a predetermined central angle and within a second wavelength range,

wherein the pixels (6) of the LC cell (5) are switchable between a state transparent to the diffuse light and the directed light and a state opaque to at least the diffuse light and are illuminated for displaying information by the diffuse light emitted by the first illumination means,

-an optical sensor layer (8) arranged below the light guiding layer body (7) having a grid-like arrangement of sensor elements (9), the sensor elements (9) being sensitive to at least the second wavelength range of light.

2. The device according to claim 1, characterized in that the surface of the sensor element (9) facing the light-conducting layer body (7) is constructed to be reflective.

3. Device according to any one of claims 1 to 2, characterized in that the central angle encloses an angle of between 0 ° and 80 °, preferably between 0 ° and 70 °, with a surface normal of the placement surface (2), and/or that the limited angular range comprises an angle of not more than 10 ° around the central angle.

4. The device according to any one of claims 1 to 3, characterized in that said first illumination means are closable during the acquisition of the skin print of the limb and/or in that said second illumination means for acquiring the skin print of the limb are openable.

5. The apparatus according to any of claims 1 to 4, characterized in that the first wavelength range for diffuse illumination and the second wavelength range for directional illumination do not have an intersection, wherein preferably the first wavelength range comprises visible light and the second wavelength range does not comprise visible light.

6. The device according to any of claims 1 to 4, wherein the second illumination means is configured to emit monochromatic light and, for separating the light of the second illumination means from the light of the first illumination means, a transmission filter as a band-pass filter is arranged between the optical sensor layer (8) and the light guiding layer body (7), the transmission filter allowing the light of the second illumination means to pass.

7. The device according to any of claims 1 to 6, characterized in that the light guiding layer body (7) comprises a substantially plate-shaped designed lower transparent layer (10) as part of the first illumination device and a substantially plate-shaped designed upper transparent layer (11) as part of the second illumination device; and comprising a first light source (12) and a second light source (13), wherein light of the first light source (12) is coupled into the lower transparent layer (10) and light of the second light source is coupled into the upper transparent layer (11), and light in the lower transparent layer (10) and in the upper transparent layer (11) is guided by means of total internal reflection, respectively, wherein, in the direction of the placement surface (2), a first out-coupling structure (14) for coupling out diffuse light is configured on a boundary surface of the lower transparent layer (10) and a second out-coupling structure (15) for coupling out directed light is configured on a boundary surface of the upper transparent layer (12), respectively.

8. The device according to claim 7, characterized in that the light of the first and second light sources (12, 13) is coupled laterally into the lower or upper transparent layer (10, 11); and/or the first and second light sources (12, 11) are combined to form a common edge lighting arrangement.

9. The device according to one of claims 1 to 6, characterized in that the light-conducting layer body (7) comprises a transparent, essentially plate-shaped design of a transparent combination layer (17), and the first lighting device comprises a first light source (12) and the second lighting device comprises a second light source (13), wherein the light of the first light source (12) is coupled into the combination layer (17) on a first narrow side (18), and the light of the second light source (13) is coupled into the combination layer (17) on a second narrow side (19) opposite to the first narrow side (18), wherein the light is guided by total internal reflection, wherein a combined out-coupling structure (20) is configured on a boundary surface of the transparent combination layer (17), the combined outcoupling structure couples out diffuse light and directional light in the direction of the placement surface (2) depending on the direction of incidence.

10. The device according to any of claims 7 to 9, wherein the light is coupled laterally into the light guiding layer body (7), characterized in that the first and second light sources (12, 13) consist of a plurality of individual light sources, wherein the emission angle of each individual light source is limited by a collimating means, preferably by a cylindrical absorbing structure (24) and/or an optical lens.

11. The device according to one of claims 7 to 10, characterized in that the lighting unit is configured to couple in the light of the first and/or second light source (12, 13) laterally through a corner.

12. The device according to any one of claims 1 to 11, characterized in that the central angle in the case of a reflection based on internal disturbed total reflection is greater than the critical angle for total reflection, otherwise the central angle is preferably 0 °.

13. The device according to any one of claims 1 to 12, characterized in that the back plate (35) of the LC cell (5) is provided with an absorption layer (38) on its side facing away from the placement face (2).

14. A method for simultaneously acquiring skin imprints of a plurality of blood-circulating skin areas of a limb placed on a resting surface (2) with a device comprising, viewed from the direction of the limb: the placement surface (2); a touch-sensitive layer (4); an LC cell (5), the LC cell (5) having pixels (6) arranged in a grid-like manner and controllable one by one; a lighting unit having a transparent light guiding layer body (7), a first lighting device for illuminating the LC cell with diffuse light in a first wavelength range, and a second lighting device for emitting directional light in a second wavelength range; and an optical sensor layer (8) having sensor elements (9) arranged in a grid-like manner and sensitive to light of at least the second wavelength range, wherein

-said LC cell (5) is illuminated by said first illumination means with diffuse light in a first wavelength range for displaying information, wherein said pixels (6) of said LC cell (5) are switchable between a state transparent to said diffuse light and a state opaque to said diffuse light,

-detecting by the touch-sensitive layer (4) whether a skin area is placed on the placing face (2) and, in case a skin area is placed, activating the sensor elements (9) of the optical sensor layer (8) and switching on the second illumination means,

-the second lighting device emits directional light within a limited angular range of not more than 20 ° around a predetermined central angle,

-detecting light reflected from the placement face (2) by means of the optical sensor layer (8) and capturing an imprint of one or more skin areas,

-after completion of the acquisition of the skin area, the optical sensor layer (8) is deactivated and the second illumination means are switched off, the acquired imprint or imprints are compared with the imprints stored in the database (26) and, if necessary, an action or actions are performed depending on the result of the comparison.

15. The method of claim 14, wherein the acquiring is repeated if a change in position of one or more skin areas or other skin areas are detected.

16. The method according to any one of claims 14 or 15, wherein a single acquisition is performed for each placed skin area.

17. The method according to any of claims 14 to 16, characterized in that the directed illumination and/or the detection of light of the second wavelength range is limited to an area where a skin area is detected to be placed by the touch-sensitive layer (8).

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